1. Field of the Invention
The present invention relates to cyclone separators provided to separate solid particles from a gas stream, and, more particularly, to a segmented vortex finder for cyclone separators such as used with circulating fluidized bed combustors and reactors.
2. Description of the Related Art
Cyclone separators connected to an outlet of pressurized fluidized bed combustors (PFBC), atmospheric fluidized bed combustors (AFBC) or circulating fluidized bed combustors (CFBC) are generally known. A cyclone separator is a device for removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Rotational effects and gravity are used to separate mixtures of solids and fluids. The cyclone separator can also be used to separate fine droplets of liquid from a gaseous stream. Cyclone separators are used in the cement, aluminum, and power industries.
A high speed rotating airflow is established within a cylindrical or conical container of the cyclone separator. Air flows in a helical pattern, beginning at the top (wide end) of the cyclone and ending at the bottom (narrow) end before exiting the cyclone in a straight stream through the center of the cyclone, up through a vortex finder and out the top. Larger (denser particles in the rotating stream have too much inertia to follow the tight curve of the stream, and strike the outside wall, then falling to the bottom of the cyclone where they can be removed. In a conical system, as the rotating flow moves towards the narrow end of the cyclone, the rotational radius of the stream is reduced, thus separating smaller and smaller particles. The cyclone geometry, together with flow rate, defines a cut point of the cyclone separator. This is the size of particle that will be removed from the stream with 50% efficiency. Particles larger than the cut point will be removed with a greater efficiency and smaller particles with a lower efficiency.
In other words, cyclone separators use cyclonic action to separate dust particles from the gas stream. In a typical cyclone separator, the dust gas stream enters at an angle and is spun rapidly. The centrifugal force created by the circular flow throws the dust particles toward the wall of the cyclone separator. After striking the wall, these particles fall into a hopper located underneath. The cyclone separator creates a dual vortex to separate coarse dust particles from fine dust particles. A main downward vortex spirals downward and carries most of the coarser dust particles. An inner ascending vortex spirals upward and carries finer dust particles.
Vortex finders (also known as dip tubes, dip legs, immersion tubes, etc.) are a common component of cyclone separators. The cyclone separator creates a dual vortex to separate coarse dust particles from fine dust particles. A main downward vortex spirals downward and carries most of the coarser dust particles. An inner ascending vortex spirals upward and carries finer dust particles exiting the cyclone separator through a vortex finder. Vortex finders in cyclone separators have a tubular shape and serve to remove the tighter volatile components (finer dust particles, such as ash) along an axis of the cyclone separator in an upward direction without impeding the upward flow by the tangentially incoming medium.
Presently, a vortex finder is in the form of a welded or segmented plate, and/or segmented interlocking pieces of metal or ceramic. Also known in the art are vortex finders, which comprise hanging segments where one segment hangs on the upper segment in a staggered manner; i.e. the center line of the lower plate is in line with the sides of the supporting segment. Currently, pockets, which support the tower segments, have a solid bottom allowing particles, such as ash, to accumulate.
Current vortex finders suffer from thermal cycling, temperature over runs, and ash build up on the segments and in the pockets of the segments. When the pockets get full of ash the segments cannot expand and contract as originally designed. This hindered expansion/contraction induce stresses in the segments and in the wedges. These stresses, over time, cause the components to warp and ultimately, to be replaced.
The reduction of maintenance and increased performance of fluidized bed combustion (FBC) boilers presents the need for an improved design of vortex finders. The need therefore exists for a vortex finder for a cyclone separator, which is suitable for adaptation to differently sized cyclones designs, and in which individual components can be easily replaced. The need also exists for a vortex finder that comprises plate segments, which reduce the possibility of deformation or braking, are stronger yet have lower weight, and provide reduced stresses at peak stress points and reduced heat loss.